Within the field of integrated circuit (IC) fabrication, there is continuing interest in finding ways to increase the density of electronic parts such as transistors, and to shrink the interconnection of these parts. Recently, there has been great interest in miniature machines which combine electrical, optical and mechanical functional features. These micromachines are frequently referred to as Micro-Electro-Mechanical-Systems (MEMS), Bio-MEMS, and Micro-Opto-Electro-Mechanical-Systems (MOEMS).
To produce the miniature electrical devices in MEMS, those skilled in the art frequently use stacks of alternating layers of conductive material, separated by electrically insulating material, with electrical interconnects between various conductive regions in the stack. Typically, the insulating material has been glass which is anodically bonded to a conductive material such as silicon. U.S. patent application Ser. No. 09/739,078, of Harald S. Gross, filed Dec. 13, 2000, assigned to the assignee of the present invention, describes an improved method of anodic bonding of a stack of conductive and electrically insulating glass layers in a single bonding step. Also, U.S. patent application Ser. No. 10/160,215 of Harald S. Gross, filed on May 28, 2002, assigned to the assignee of the present invention, describes a method of producing electrical interconnects within such a stack of layers.
There is a clear need for a cheap and efficient method of fabricating microelectronic structures which can perform at the temperature capability of silicon, which can be machined to silicon tolerances.
One technology which is used within the MEMS and MOEMS industry is microcolumns. Microcolumns are high-aspect-ratio micromechanical structures including microlenses and deflectors. The microlenses are frequently multilayers of silicon chips (with membrane windows for the lens electrodes) or silicon membranes spaced apart by 100–500 μm thick insulating layers. The lenses have bore diameters that vary from a few to several hundred μm. For optimum performance, the structural alignment accuracy between the components should be in the few μm range. Particularly in the telecommunications industry, in order to achieve high performance, the components like glass fibers are precisely aligned and subsequently bonded.
In the past, there have been several approaches to achieve alignment accuracy. In most cases highly sophisticated tools which utilize marks on the surface of each micro-fabricated structure are used to align the components using an optical inspection tool. However such alignment equipment is very expensive. Also, a satisfying throughput rate can not be achieved with such tools if more than two components need to be aligned. Generally, the optical tool aligns just two components which are subsequently bonded. When three components are involved, the optical tool follows the same procedure; this means that the first two components are aligned and bonded and then the bonded components are then aligned with and bonded to a third component. Therefore, the process itself becomes a serial aligning and bonding method. It can be seen that efficiency of such alignment tool is low. The throughput rate is a function of the number of necessary repetitions in respect to a two component system. Moreover, there is a fast growing demand for applications that require the assembly of more than just two components, and for those applications alignment using optical system would be impractical.
U.S. Pat. No. 6,281,508 B1 issued Aug. 28, 2001 to Lee et al., and assigned to the Assignee of the present invention describes a method and the associated apparatus for alignment and assembly of microlenses and microcolumns. In the Lee et al. patent, aligning structures such as rigid fibers are used to precisely align multiple microlens components. Alignment openings are formed in the microlens components and standard optical fibers are threaded through the openings in each microlens component as they are stacked. However, the patent does not describe how the glass fibers are moved practically during the alignment procedure. Also, the patent does not mention how to achieve the necessary parallelism of the fibers. The second method described in the patent involves a “snap-mechanism” of the fiber into holes of the components, which have a smaller size than the fiber itself. In addition, the method described in this patent is a serial assembly process rather than a parallel assembly. Therefore, the method could run into the problem of throughput efficiency described above. Moreover, the assembly explained in this patent is uses an alternating layers of microlens components with glass which the present invention is trying to avoid.
There is clearly a need for a cheap and efficient method of aligning components of MEMS, bio-MEMS, and MOEMS structures to meet the precision and accuracy requirements described above.